Method of forming phase change material layer and method of fabricating phase change memory device

ABSTRACT

A method of forming a phase change material layer and a method of fabricating a phase change memory device, the method of forming a phase change material layer including forming an amorphous germanium layer by supplying a germanium containing first source into a reaction chamber; cutting off supplying the first source after forming the amorphous germanium layer; and forming amorphous Ge 1-x Te x  (0&lt;x≦0.5) such that forming the amorphous Ge 1-x Te x  (0&lt;x≦0.5) includes supplying a tellurium containing second source into the reaction chamber after cutting off supplying the first source.

BACKGROUND

1. Field

Embodiments relate to a method of forming a phase change material layerand a method of fabricating a phase change memory device.

2. Description of Related Art

In general, semiconductor memory devices may be classified as volatilememory devices and nonvolatile memory devices. The nonvolatile memorydevices may retain their stored data even when their power supplies areinterrupted. Nonvolatile memory devices may include, e.g., programmableROM (PROM), erasable PROM (EPROM), electrically EPROM (EEPROM), andflash memory. Recently, there has been an increasing demand fornon-volatile memory devices that can be electrically programmed anderased.

Variable resistance memory devices, e.g., resistive random access memory(ReRAM) and phase-change random access memory (PRAM), have beendeveloped as nonvolatile memory devices. Materials constituting variableresistance semiconductor memory devices may be characterized in thattheir resistance may be varied by application of current/voltage, andmay be maintained even when the current or voltage is cut off.

PRAM uses a phase change material, e.g., a chalcogenide material. Thephase change material may be in either a crystalline state or anamorphous state. If a phase change material in an amorphous state isheated to a temperature between a crystallization temperature and amelting point for a predetermined time and then cooled, it maytransition to the crystalline state from the amorphous state (setprogramming). On the other hand, if the phase change material is heatedto a relatively high temperature, e.g., above the melting point, andquickly cooled, it may transition to an amorphous state from acrystalline state (reset programming).

Several approaches have been taken to apply write current of relativelygreat value during reset programming. One of the approaches is that acontact area between a heating electrode and the phase change materialmay be reduced to increase an effective current density. After forming aminute hole to expose a bottom electrode, a phase change material may beformed in the hole to reduce a contact area between the heatingelectrode and the phase change material.

SUMMARY

Embodiments are directed to a method of forming a phase change materiallayer and a method of fabricating a phase change memory device, whichrepresent advances over the related art.

It is a feature of an embodiment to provide a method of forming a phasechange material layer that is capable of being deposited minutely andconformally without voids.

At least one of the above and other features and advantages may berealized by providing a method of forming a phase change material layer,the method including forming an amorphous germanium layer by supplying agermanium containing first source into a reaction chamber; cutting offsupplying the first source after forming the amorphous germanium layer;and forming amorphous Ge_(1-x)Te_(x) (0<x≦0.5) such that forming theamorphous Ge_(1-x)Te_(x) (0<x≦0.5) includes supplying a telluriumcontaining second source into the reaction chamber after cutting offsupplying the first source.

The amorphous Ge_(1-x)Te_(x) (0<x≦0.5) may be formed at a temperature ofabout 300° C. or greater.

The amorphous Ge_(1-x)Te_(x) (0<x≦0.5) may be formed at a temperature ofabout 300° C. to about 400° C.

The first source may include at least one of an amide ligand, aphosphanido ligand, an alkoxide ligand, and a thiolate ligand.

The method may further include supplying a reactive gas into thereaction chamber, the reactive gas including at least one of ammonia,primary amine, diazene, and hydrazine.

The method may further include supplying an antimony containing thirdsource into the reaction chamber.

The third source may be supplied after supplying the second source.

The method may further include sequentially supplying additional secondsource and first source after supplying the third source.

The method may further include supplying additional second source at thesame time as supplying the third source.

The third source and second source may be supplied at the same time.

The method may further include forming an amorphous layer ofSb_(1-x)Te_(x) (0<x<1) on the amorphous Ge_(1-x)Te_(x) (0<x≦0.5).

The method may further include purging the reaction chamber betweensupplying sources.

At least one of the above and other features and advantages may also berealized by providing a method of fabricating a phase change memorydevice, the method including providing a substrate having a bottomelectrode; forming an insulating layer having an opening such that theopening exposes the bottom electrode; forming an amorphous germaniumlayer by supplying a germanium containing first source into the opening;cutting off supplying the first source after forming the amorphousgermanium layer; and forming amorphous Ge_(1-x)Te_(x) (0<x≦0.5) suchthat forming the amorphous Ge_(1-x)Te_(x) (0<x≦0.5) includes supplying atellurium containing second source onto the substrate to after cuttingoff supplying the first source.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages will become more apparent tothose of ordinary skill in the art by describing in detail exemplaryembodiments with reference to the attached drawings, in which:

FIG. 1 illustrates a flowchart of a method of forming a phase changematerial layer according to an embodiment;

FIG. 2 illustrates a source supply diagram of the method of forming aphase change material layer of FIG. 1;

FIG. 3A illustrates a surface SEM image of a comparative phase changematerial layer;

FIG. 3B illustrates a surface SEM image of a phase change material layerformed according to the method of FIG. 1;

FIG. 4 illustrates a flowchart of a method of forming a phase changematerial layer according to another embodiment;

FIG. 5 illustrates a source supply diagram of the method of forming aphase change material layer of FIG. 4;

FIG. 6 illustrates a surface SEM image of a phase change material formedaccording to the method of FIG. 4;

FIG. 7 illustrates a flowchart of a method of forming a phase changematerial layer according to yet another embodiment;

FIG. 8 illustrates a source supply diagram of the method of forming aphase change material layer of FIG. 7;

FIG. 9 illustrates a surface SEM image of a phase change material formedaccording to the method of FIG. 7;

FIGS. 10 to 13 illustrate stages in a method of forming a phase changememory device according to an embodiment;

FIG. 14 illustrates a result of an endurance test for a phase changememory device formed according to the method of an embodiment;

FIG. 15 illustrates a memory card system including phase change memorydevices according to an embodiment; and

FIG. 16 illustrates an electronic system including phase change memorydevices according to an embodiment.

DETAILED DESCRIPTION

Korean Patent Application No. 10-2009-0018138, filed on Mar. 3, 2009, inthe Korean Intellectual Property Office, and entitled: “Method ofForming Phase Change Material Layer,” is incorporated by referenceherein in its entirety.

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

In the drawing figures, the dimensions of layers and regions may beexaggerated for clarity of illustration. It will also be understood thatwhen a layer or element is referred to as being “on” another layer orsubstrate, it can be directly on the other layer or substrate, orintervening layers may also be present. In addition, it will also beunderstood that when a layer is referred to as being “between” twolayers, it can be the only layer between the two layers, or one or moreintervening layers may also be present. Like reference numerals refer tolike elements throughout.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one element, component, region, layer or section fromanother region, layer or section. Thus, a first element, component,region, layer or section discussed below could be termed a secondelement, component, region, layer or section without departing from theteachings of the inventive concept.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Referring to FIGS. 1 and 2, a method of forming a phase change materiallayer according to an embodiment will now be described in detail. In animplementation, the phase change material layer may be formed by atomiclayer deposition (ALD). A substrate may be loaded into a reactionchamber (S100). The substrate may be a semiconductor-based substrate.The substrate may include a conductive area and/or an insulating area.The conductive area may include a conductive layer. The conductive layermay be made of, e.g., titanium, titanium nitride, aluminum, thallium,thallium nitride, and/or titanium aluminum nitride. The insulating areamay include an inorganic layer. The inorganic layer may be made of,e.g., silicon oxide, titanium oxide, aluminum oxide, zirconium oxide,and/or hafnium oxide. In an implementation, the substrate may be heatedto a temperature of, e.g., about 300 degrees centigrade (° C.) orgreater. In another implementation, the substrate may be heated to atemperature of, e.g., about 300° C. to about 400° C.

For a time T1, a first reactive gas may be supplied into the reactionchamber (S110). The first reactive gas may include a functional grouprepresented by —NR₁R₂ (wherein R₁ and R₂ may each independently be,e.g., H, CH₃, C₂H₅, C₃H₇, C₄H₉, or Si(CH₃)₄). The first reactive gas mayinclude, e.g., an —NH₂ group. In an implementation, the first reactivegas may include, e.g., ammonia, primary amine, diazene, and hydrazine.In another implementation, the first reactive gas may include, e.g., NH₃(ammonia) or N₂H₂ (diazene).

A first source, containing germanium, may be supplied into the reactionchamber before, after, or at the same time the first reactive gas issupplied. For example, for the time T1, the first source may besupplied. The first source may be carried by a first carrier gas. Thefirst source may be a Ge(II) source (wherein the “Ge(II)” means that anoxidation state of germanium is +2). The first source may include, e.g.,amide ligand, phosphanido ligand, alkoxide ligand, and/or thiolateligand. In an implementation, the first source may include, e.g.,Ge[(iPr)₂Amid(Bu)]₂, Ge(MABO)₂, and/or Ge(MAPO)₂. In anotherimplementation, the first source may include only a germanium containingcompound. In yet another implementation, the first source may consistessentially of the germanium containing compound. As a result, a thinfilm of N-doped amorphous germanium may be formed on the substrate.

For a time T2, the supply of the first source may be cut off and thefirst carrier gas and/or the first reactive gas may continue to besupplied into the reaction chamber. In an implementation, the firstreactive gas may also be cut off at time T2. Thus, physically adsorbedfirst source and unreacted first source may be purged (S120).

For a time T3, a second source may be supplied into the reaction chamber(S130). The second source may include tellurium (Te). In animplementation, the second source may include, e.g., Te(CH₃)₂,Te(C₂H₅)₂, Te(n-C₃H₇)₂, Te(i-C₃H₇)₂, Te(t-C₄H₉)₂, Te(i-C₄H₉)₂,Te(CH═CH₂)₂, Te(CH₂CH═CH₂)₂, and/or Te[N(Si(CH₃)₃)₂]₂. The second sourcemay be carried by a second carrier gas. A second reactive gas may besupplied before, after, or at the same time the second source issupplied. The second reactive gas may include, e.g., hydrogen (H₂),oxygen (O₂), ozone (O₃), steam (H₂O), silane (SiH₄), diborane (B₂H₆),hydrazine (N₂H₄), primary amine, and/or ammonia (NH₃). As a result, aphase change material layer of N-doped amorphous Ge_(1-x)Te_(x)(0<x≦0.5), i.e., having a tellurium content of about 50 percent or less,may be formed on the substrate. In other words, the N-doped amorphousGe_(1-x)Te_(x) (0<x≦0.5) may have a up to 50 percent Te, but not above.

For a time T4, the supply of the second source may be cut off and thesecond carrier gas and/or the second reactive gas may continue to besupplied into the reaction chamber. In an implementation, the secondreactive gas may also be cut off at time T4. Thus, physically adsorbedsecond source and unreacted second source may be purged (S140).

For a time T5, a third source may be supplied into the reaction chamber(S150). The third source may include antimony (Sb). In animplementation, the third source may include, e.g., Sb(CH₃)₃, Sb(C₂H₅)₃,Sb(i-C₃H₇)₃, Sb(n-C₃H₇)₃, Sb(i-C₄H₉)₃, Sb(t-C₄H₉)₃, Sb(N(CH₃)₂)₃,Sb(N(CH₃)(C₂H₅))₃, Sb(N(C₂H₅)₂)₃, Sb(N(i-C₃H₇)₂)₃, and/orSb[N(Si(CH₃)₃)₂]₃. The third source may be carried by a third carriergas. A third reactive gas may be supplied before, after, or at the samethe third source is supplied. The third reactive gas may include, e.g.,hydrogen (H₂), oxygen (O₂), ozone (O₃), steam (H₂O), silane (SiH₄),diborane (B₂H₆), hydrazine (N₂H₄), primary amine, and/or ammonia (NH₃).As a result, a layer of Sb_(1-x)Te_(x) (0<x<1) may be formed on thelayer of amorphous Ge_(1-x)Te_(x) (0<x≦0.5) to form a phase changematerial layer of N-doped amorphous Ge—Sb—Te on the substrate.

For a time T6, the supply of the third source may be cut off and thethird carrier gas and/or the third reactive gas may continue to besupplied into the reaction chamber. In an implementation, the thirdreactive gas may also be cut off at time T6. Thus, physically adsorbedthird source and unreacted third source may be purged (S160).

For a time T7, the second source may again be supplied into the reactionchamber (S170). As described above, the second source may includetellurium (Te). In an implementation, the additional second source mayinclude, e.g., Te(CH₃)₂, Te(C₂H₅)₂, Te(n-C₃H₇)₂, Te(i-C₃H₇)₂,Te(t-C₄H₉)₂, Te(i-C₄H₉)₂, Te(CH═CH₂)₂, Te(CH₂CH═CH₂)₂, and/orTe[N(Si(CH₃)₃)₂]₂. The second source may be carried by a fourth carriergas. A fourth reactive gas may be supplied before, after, or at the sametime the second source is supplied. The fourth reactive gas may include,e.g., hydrogen (H₂), oxygen (O₂), ozone (O₃), steam (H₂O), silane(SiH₄), diborane (B₂H₆), hydrazine (N₂H₄), primary amine, and/or ammonia(NH₃).

For a time T8, the supply of the additional second source may be cut offand the fourth carrier gas and/or the fourth reactive gas may continueto be supplied into the reaction chamber. In an implementation, thefourth reactive gas may also be cut off at time T8. Thus, physicallyadsorbed second source and an unreacted second source may be purged(S180).

In an implementation, the sequence of S110 to S180 (T1-T8) may representone cycle. The cycle may be one or more additional times, depending on adesired thickness of the phase change material layer. The phase changematerial layer of N-doped amorphous Ge—Sb—Te according to an embodimentmay have a superior characteristic in that, e.g., a crystallinestructure may not be visible (see FIG. 3B).

There may be difficulty in reacting antimony from the third sourceprovided during S150 with germanium from the first source providedduring S110. Accordingly, the tellurium (second) source is preferablysupplied again during S170.

Referring to FIGS. 4 and 5, a method of forming a phase change materiallayer according to another embodiment will now be described in detail.In order to avoid repetition, the following explanations relate only toaspects that are different from FIGS. 1 and 2.

A substrate may be loaded into a reaction chamber (S200). The substratemay be a semiconductor-based substrate. In an implementation, thesubstrate may be heated to a temperature of, e.g., about 300° C. orgreater. In another implementation, the substrate may be heated to atemperature of, e.g., about 300° C. to about 400° C.

For a time T1, a first reactive gas may be supplied into the reactionchamber (S210). The first reactive gas may include a functional grouprepresented by —NR₁R₂ (wherein R₁ and R₂ may each independently be H,CH₃, C₂H₅, C₃H₇, C₄H₉, and/or Si(CH₃)₄). In an implementation firstreactive gas may include, e.g., an —NH₂ group. In anotherimplementation, the first reactive gas may include, e.g., ammonia,primary amine, diazene, and/or hydrazine.

A first source, containing germanium, may be supplied into the reactionchamber before, after, or at the same time the first reactive gas issupplied. For example, for the time T1, the first source may besupplied. The first source may be carried by a first carrier gas. Thefirst source may be a Ge(II) source. In an implementation, first sourcemay include, e.g., amide ligand, phosphanido ligand, alkoxide ligand,and/or thiolate ligand. In another implementation, the first source mayinclude, e.g., Ge[(iPr)₂Amid(Bu)]₂, Ge(MABO)₂, and/or Ge(MAPO)₂. As aresult, a thin film of N-doped amorphous germanium may be formed on thesubstrate.

For a time T2, the supply of the first source may be cut off and thefirst carrier gas and/or the first reactive gas may continue to besupplied into the reaction chamber. In an implementation, the firstreactive gas may also be cut off at time T2. Thus, physically adsorbedfirst source and unreacted first source may be purged (S220).

For a time T3, a second source may be supplied into the reaction chamber(S230). The second source may include tellurium (Te). In animplementation, the second source may include, e.g., Te(CH₃)₂,Te(C₂H₅)₂, Te(n-C₃H₇)₂, Te(i-C₃H₇)₂, Te(t-C₄H₉)₂, Te(i-C₄H₉)₂,Te(CH═CH₂)₂, Te(CH₂CH═CH₂)₂, and/or Te[N(Si(CH₃)₃)₂]₂. The second sourcemay be carried by a second carrier gas. A second reactive gas may besupplied before, after, or at the same time the second source issupplied. As a result, a phase change material layer of N-dopedamorphous Ge_(1-x)Te_(x) (0<x≦0.5),), i.e., having a tellurium contentof about 50 percent or less, may be formed on the substrate.

For a time T4, the supply of the second source may be cut off and thesecond carrier gas and/or the second reactive gas may continue to besupplied into the reaction chamber. In an implementation, the secondreactive gas may also be cut off at time T4. Thus, physically adsorbedsecond source and unreacted second source may be purged (S240).

For a time T5, a third source and additional second source may besimultaneously supplied into the reaction chamber (S250). The thirdsource may include antimony (Sb). In an implementation, the third sourcemay include, e.g., Sb(CH₃)₃, Sb(C₂H₅)₃, Sb(i-C₃H₇)₃, Sb(n-C₃H₇)₃,Sb(i-C₄H₉)₃, Sb(t-C₄H₉)₃, Sb(N(CH₃)₂)₃, Sb(N(CH₃)(C₂H₅))₃,Sb(N(C₂H₅)₂)₃, Sb(N(i-C₃H₇)₂)₃ or Sb[N(Si(CH₃)₃)₂]₃. Sb(CH₃)₃,Sb(C₂H₅)₃, Sb(i-C₃H₇)₃, Sb(n-C₃H₇)₃, Sb(i-C₄H₉)₃, Sb(t-C₄H₉)₃,Sb(N(CH₃)₂)₃, Sb(N(CH₃)(C₂H₅))₃, Sb(N(C₂H₅)₂)₃, Sb(N(i-C₃H₇)₂)₃, and/orSb[N(Si(CH₃)₃)₂]₃. The third source and additional second source may becarried by a third carrier gas. A third reactive gas may be suppliedbefore, after, or at the same the second and third sources are supplied.As a result, a layer of Sb_(1-x)Te_(x) (0<x<1) may be formed on thelayer of amorphous Ge_(1-x)Te_(x) (0<x≦0.5) to form a phase changematerial layer of N-doped amorphous Ge—Sb—Te on the substrate.

For a time T6, the supply of the second and third sources may be cut offand the third carrier gas and/or the third reactive gas may continue tobe supplied into the reaction chamber. In an implementation, the thirdreactive gas may also be cut off at time T6. Thus, physically adsorbedsecond and third source as well as unreacted second and third source maybe purged (S260).

In an implementation, the sequence of S210 to S260 (T1-T6) may representone cycle. The cycle may be performed one or more additional times,depending on a desired thickness of the phase change material layer. Thephase change material layer of N-doped amorphous Ge—Sb—Te according tothe present embodiment may have a superior characteristic in that, e.g.,a crystalline structure may not be visible (see FIG. 6).

Referring to FIGS. 7 and 8, a method of forming a phase change materiallayer according to yet another embodiment will now be described indetail. In order to avoid repetition, the following explanations relateonly to aspects that are different from FIGS. 1 and 2.

A substrate may be loaded into a reaction chamber (S200). The substratemay be a semiconductor-based substrate. The substrate may be heated to atemperature of, e.g., greater than about 300° C. In an implementation,the substrate may be heated to a temperature of, e.g., about 300° C. toabout 400° C.

For a time T1, a first reactive gas may be supplied into the reactionchamber (S310). The first reactive gas may include a functional grouprepresented by —NR₁R₂ (wherein R₁ and R₂ may each independently be,e.g., H, CH₃, C₂H₅, C₄H₉, and/or Si(CH₃)₄). In an implementation, thefirst reactive gas may include, e.g., an —NH₂ group. In anotherimplementation, the first reactive gas may include, e.g., ammonia,primary amine, diazene, and/or hydrazine.

A first source, containing germanium, may be supplied into the reactionchamber before, after, or at the same time as the first reactive gas issupplied. For example, for the time T1, the first source may besupplied. The first source may be carried by a first carrier gas. Thefirst source may be a Ge(II) source. The first source may include, e.g.,amide ligand, phosphanido ligand, alkoxide ligand, and/or thiolateligand. In an implementation, the first source may include, e.g.,Ge[(iPr)₂Amid(Bu)]₂, Ge(MABO)₂, and/or Ge(MAPO)₂. As a result, a thinfilm of N-doped amorphous germanium may be formed on the substrate.

For a time T2, the supply of the first source may be cut off and thefirst carrier gas and/or the first reactive gas may continue to besupplied into the reaction chamber. In an implementation, the fourthreactive gas may also be cut off at time T2. Thus, physically adsorbedfirst source and unreacted first source may be purged (S320).

For a time T3, a second source and a third source may be simultaneouslysupplied into the reaction chamber (S330). The second source may includetellurium (Te). In an implementation, the second source may include,e.g., Te(CH₃)₂, Te(C₂H₅)₂, Te(n-C₃H₇)₂, Te(i-C₃H₇)₂, Te(t-C₄H₉)₂,Te(i-C₄H₉)₂, Te(CH═CH₂)₂, Te(CH₂CH═CH₂)₂, and/or Te[N(Si(CH₃)₃)₂]₂. Thethird source may include antimony (Sb). In an implementation, the thirdsource may include, e.g., Sb(CH₃)₃, Sb(C₂H₅)₃, Sb(i-C₃H₇)₃, Sb(n-C₃H₇)₃,Sb(i-C₄H₉)₃, Sb(t-C₄H₉)₃, Sb(N(CH₃)₂)₃, Sb(N(CH₃)(C₂H₅))₃,Sb(N(C₂H₅)₂)₃, Sb(N(i-C₃H₇)₂)₃ or Sb[N(Si(CH₃)₃)₂]₃. Sb(CH₃)₃,Sb(C₂H₅)₃, Sb(i-C₃H₇)₃, Sb(n-C₃H₇)₃, Sb(i-C₄H₉)₃, Sb(t-C₄H₉)₃,Sb(N(CH₃)₂)₃, Sb(N(CH₃)(C₂H₅))₃, Sb(N(C₂H₅)₂)₃, Sb(N(i-C₃H₇)₂)₃, and/orSb[N(Si(CH₃)₃)₂]₃. The second and third sources may be carried by asecond carrier gas. A second reactive gas may be supplied before, after,or at the same time the second and third sources are supplied. As aresult, a layer of Sb_(1-x)Te_(x) (0<x<1) may be formed on a layer ofamorphous Ge_(1-x)Te_(x) (0<x≦0.5) to form a phase change material layerof N-doped amorphous Ge—Sb—Te on the substrate.

For a time T4, the supply of the second and third sources may be cut offand the second carrier gas and/or the second reactive gas may continueto be supplied into the reaction chamber. In an implementation, thesecond reactive gas may also be cut off at time T4. Thus, physicallyadsorbed second and third source as well as unreacted second and thirdsource may be purged (S340).

In an implementation, the sequence of S310 to S340 (T1-T4) may representone cycle. The cycle may be performed one or more additional times,depending on a desired thickness of the phase change material layer. Thephase change material layer of N-doped amorphous Ge—Sb—Te according tothe present embodiment may exhibit a superior characteristic in that,e.g., a crystalline structure may not be visible (see FIG. 9).

In the above described embodiments, the first to third sources may becarried by the first to fourth carrier gases. Each of the carrier gasesmay be an inert gas including, e.g., argon (Ar), helium (He), and/ornitrogen (N₂). In an alternative implementation, the first to thirdsources may be supplied into the reaction chamber after being dissolvedin respective solvents and rapidly vaporized using a vaporizer.

In the above described embodiments, the reactive gases may be suppliedsimultaneously with the sources. However, the embodiments are notlimited thereto. For example, a thin film may be deposited by thesources without the respective reactive gases and then treated withplasma of the reactive gases (e.g., NH₃ plasma).

Generally, when a layer of N-doped Ge—Te, (which may be useful as aphase change material is formed), it may be difficult to adjust a ratioof Ge and Te. For example, while N-doped Ge—Te (N—Ge—Te) is amorphousand may be conformally deposited when the content of Ge is relativelylarge, N-doped Ge (N—Ge), formed by bonding to N the Ge that remainsunbonded to Te, is a nonconductor and has high resistance. Thus, if thecontent of the N—Ge of the phase change material is higher than that ofthe N—Ge—Te, resistance may undesirably increase. Thus, the phase changematerial may not be suitable for a PRAM. A phase change material layermay be formed by simultaneously providing a Ge(II) source and Te source.However, when a phase change material layer is formed by suchsimultaneous supply at a process temperature of, e.g., 300° C. orhigher, a ratio of Te to Ge—Te may be greater than 50 percent. Thus, thegeneral phase change material layer may become undesirably crystalline(see FIG. 3A). Further, although no void may be observed in a hole at aninitial deposition, void(s) may be formed by annealing during asubsequent integration process. The phase change material layer formedaccording to an embodiment may not become crystalline and also may notform voids during subsequent manufacturing processes.

In contrast, according to embodiments, times of supplying the firstsource, containing germanium, and the second source, containingtellurium, may be controlled independently. In other words, the firstsource and the second source may be supplied to the substrate fordifferent durations. Therefore, a ratio of Te to Ge—Te may be adjustedto below about 50 percent even at a high temperature, e.g., above about300° C. In an implementation, the ratio of Te to Ge—Te may be adjustedto be, e.g., about 50 percent, less than 50 percent, or less than orequal to 50 percent. Thus, the phase change material may becomeamorphous and may be deposited minutely and conformally (see FIG. 3B,FIG. 6, and FIG. 9). Further, a void may not be formed even whenannealing is conducted during a subsequent integration process.Accordingly, a contact area between a heating electrode and the phasechange material layer may be reduced, thus increasing an effectivecurrent density and a magnitude of a write current during, e.g., resetprogramming.

Referring to FIGS. 10 to 13, a method of fabricating a phase changememory device according to an embodiment will now be described below indetail.

As illustrated in FIG. 10, a semiconductor substrate 101 includingwordlines (not illustrated) and selection elements (not illustrated) maybe provided. The wordlines may include a line-shaped impurity-dopedregion. The selection element may include a diode or a transistor. Afirst interlayer dielectric 110 may be formed on the semiconductorsubstrate 101.

A bottom electrode 112 may be formed on the first interlayer dielectric110. The bottom electrode 112 may include, e.g., titanium, titaniumnitride, titanium aluminum nitride, tantalum, tantalum nitride,tungsten, tungsten nitride, molybdenum nitride, niobium nitride,titanium silicon nitride, titanium boron nitride, zirconium siliconnitride, tungsten silicon nitride, tungsten boron nitride, zirconiumaluminum nitride, molybdenum aluminum nitride, tantalum silicon nitride,tantalum aluminum nitride, titanium tungsten, titanium aluminum,titanium oxynitride, titanium aluminum oxynitride, tungsten oxynitride,and/or tantalum oxynitride.

Referring to FIG. 11, an insulating layer 120 may be formed on thebottom electrode 112. The insulating layer 120 may be formed of, e.g.,silicon oxide such as borosilicate glass (BSG), phosphosilicate glass(PSG), borophosphosilicate glass (BPSG), plasma-enhancedtetraethylorthosilicate (PE-TEOS), and/or high-density plasma (HDP).

An opening 122 may be formed in the insulating layer 120 to expose aportion of the bottom electrode 112. A spacer insulating layer (notillustrated) may be formed in the opening 122 and then anisotropicallyetched to expose the bottom electrode 112, thereby forming a spacer 124on a sidewall of the opening 120. The spacer 124 may allow an effectivesize of the opening 120 to become smaller than a resolution limit of aphotolithography process.

Referring to FIG. 12, a Ge—Sb—Te phase change material layer 130 may beformed by, e.g., atomic layer deposition (ALD), according to the abovedescribed embodiments to fill the opening 122. A process temperature maybe about 300° C. to about 400° C. A thin film of amorphousGe_(1-x)Te_(x)(0<x≦0.5) may be formed; and then a layer of amorphousSb_(1-x)Te_(x)(0<x<1) may be formed thereon. Thus, a phase changematerial layer of N-doped amorphous Sb_(1-x)Te_(x)(0<x<1) may be formed.Since the phase change material layer may be an amorphous layer even ata high temperature, it may fill a minute and small-sized opening withoutan undesirable void.

Referring to FIG. 13, the phase change material layer 130 may beplanarized to form a phase change material pattern 132. A top electrode140 may be formed on the phase change material pattern 132. The phasechange material layer 130 may be planarized by, e.g., etch-back orchemical mechanical polishing (CMP). A phase change resistor may beformed, the phase change resistor including the bottom electrode 112,the top electrode 140, and the phase change material pattern 132 betweenthe bottom and top electrodes 112 and 140.

A reliability of a phase change memory device according to an embodimentwas estimated. Referring to FIG. 14, an excellent endurance wasexhibited in which a constant resistance characteristic was maintaineddespite being cycled (i.e., set and reset) up to 10⁸ times.

Referring to FIG. 15, a memory card system 200 including phase changememory devices according to an embodiment will now be described. Thememory card system 200 may include a controller 210, a memory 220, andan interface 230. The controller 210 may include, e.g., amicroprocessor, a digital signal processor, a microcontroller, or thelike. The memory 220 may be used to, e.g., store a command executed bythe controller 210 and/or user data. The memory 220 may include not onlyphase change memory devices formed according to the above describedembodiments, but also, e.g., a random accessible nonvolatile memorydevice and/or various types of memory devices. The controller 210 andthe memory 220 may be configured to transfer and receive the commandand/or the data. The interface 230 may serve to input/output externaldata. The memory card system 200 may be, e.g., a multimedia card (MMC),a secure digital card (SD), or a portable data storage.

Referring to FIG. 16, an electronic system 300 including phase changedevices according to an embodiment will now be described. The electronicsystem 300 may include a processor 310, a memory device 320, and aninput/output device (I/O) 330. The processor 310, the memory device 320,and the I/O 330 may be connected through a bus 340. The memory 320 mayreceive control signals, e.g., RAS*, WE*, and CAS*, from the processor310. The memory 320 may be used to store data accessed through the bus340 and/or a command executed by the controller 310. The memory 320 mayinclude a variable resistance memory device according to an embodiment.It will be appreciated by those skilled in the art that an additionalcircuit and control signals may be applied for detailed realization andmodification of the embodiments.

The electronic system 300 may be used in, e.g., computer systems,wireless communication devices (e.g., personal digital assistants (PDA),laptop computers, web tablets, mobile phones, and cellular phones),digital music players, MP3 players, navigators, solid-state disks (SSD),household appliances, and/or any components capable of transmitting andreceiving data in a wireless environment.

Exemplary embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation.Accordingly, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made without departingfrom the spirit and scope of the present invention as set forth in thefollowing claims.

1. A method of forming a phase change material layer, the methodcomprising: forming an amorphous germanium layer by supplying agermanium containing first source into a reaction chamber; cutting offsupplying the first source after forming the amorphous germanium layer;and forming amorphous Ge_(1-x)Te_(x) (0<x≦0.5) such that forming theamorphous Ge_(1-x)Te_(x) (0<x≦0.5) includes supplying a telluriumcontaining second source into the reaction chamber after cutting offsupplying the first source.
 2. The method as claimed in claim 1, whereinthe amorphous Ge_(1-x)Te_(x) (0<x≦0.5) is formed at a temperature ofabout 300° C. or greater.
 3. The method as claimed in claim 2, whereinthe amorphous Ge_(1-x)Te_(x) (0<x≦0.5) is formed at a temperature ofabout 300° C. to about 400° C.
 4. The method as claimed in claim 1,wherein the first source includes at least one of an amide ligand, aphosphanido ligand, an alkoxide ligand, and a thiolate ligand.
 5. Themethod as claimed in claim 4, further comprising supplying a reactivegas into the reaction chamber, the reactive gas including at least oneof ammonia, primary amine, diazene, and hydrazine.
 6. The method asclaimed in claim 1, further comprising supplying an antimony containingthird source into the reaction chamber.
 7. The method as claimed inclaim 6, wherein the third source is supplied after supplying the secondsource.
 8. The method as claimed in claim 7, further comprisingsequentially supplying additional second source and first source aftersupplying the third source.
 9. The method as claimed in claim 7, furthercomprising supplying additional second source at the same time assupplying the third source.
 10. The method as claimed in claim 6,wherein the third source and second source are supplied at the sametime.
 11. The method as claimed in claim 1, further comprising formingan amorphous layer of Sb_(1-x)Te_(x) (0<x<1) on the amorphousGe_(1-x)Te_(x) (0<x≦0.5).
 12. The method as claimed in claim 1, furthercomprising purging the reaction chamber between supplying sources. 13.(canceled)